1. Field of the Invention
The present invention relates to a metal-bonded grinding tool having abrasive grains fixed by metal, and also to a manufacturing method for such a metal-bonded grinding tool.
2. Description of the Related Art
A conventional metal-bonded grinding tool is manufactured by mixing abrasive grains with metal powder, next forming the mixture into a given shape, and finally sintering the formed mixture integrally with a base or body of the tool to thereby fix the abrasive grains to the base (impregnated sintered tool). As another manufacturing method for a conventional metal-bonded grinding tool, abrasive grains are first placed on a base or body of the tool, and nickel plating (electrically or chemically) is applied so as to cover the abrasive grains with nickel metal deposited, thereby mechanically fixing the abrasive grains through the deposited nickel metal to the base.
In these conventional metal-bonded grinding tools, the abrasive grains are simply mechanically fixed to the metal bond matrix, and there is a limit in force of retaining the abrasive grains by the metal bond matrix. Accordingly, there is a possibility that the abrasive grains may be separated from the metal bond matrix in a relatively short period of time. Furthermore, since the amount of projection of each abrasive grain is small, the exposed surface of the metal bond matrix comes into contact with a workpiece. Accordingly, contact resistance and erosion wear tend to occur on the exposed surface of the metal bond matrix, causing a problem that the grinding tool is lacking in grinding ability and durability.
Japanese Patent Laid-open No. Sho 63-251170 discloses a cutting tool manufactured by fixing abrasive grains through nickel plating, and next covering the nickel plating with a material having a strength larger than that of the metal bond matrix, so as to retard the separation of the abrasive grains in use of the tool. This covering layer is formed by plasma spraying of metal, carbide, oxide, nitride, etc. However, the formation of the covering layer by plasma spraying may give rise to undue covering of the surface of the abrasive grains with the covering layer. It is therefore necessary to perform a finishing step of removing the covering layer formed on the surface of the abrasive grains by dressing or the like. Further, also in this grinding tool described in this publication, the abrasive grains are simply mechanically fixed by the nickel plating, so that it is difficult to obtain a sufficient force of retaining the abrasive grains to prevent the separation of the abrasive grains.
The metal bond matrix incurs erosion wear due to the contact with a workpiece to expose the abrasive grains. However, in the conventional grinding tools, no chemical bond is present between the metal bond matrix and the abrasive grains, and the abrasive grains are therefore easily separated from the metal bond matrix. Accordingly, the effective use efficiency of the abrasive grains is quite low, the grinding is unstable, and the life of the tool is quite short.
Further, a metal-bonded grinding tool in general has a self-dressing property by the chips of a workpiece to expose the abrasive grains from the surface of the metal bond matrix. Accordingly, the grinding performance is remarkably reduced according to the combination of the workpiece and the metal bond matrix. The amount and shape of the chips may vary according to working conditions, so that the grinding performance may vary according to the matching between the property of the workpiece, the property of the metal bond matrix, and the working conditions.
It is therefore an object of the present invention to provide a metal-bonded grinding tool and a manufacturing method therefor which can ensure a long life and a high grinding performance by strongly retaining the abrasive grains by the metal bond matrix independently of the property of the workpiece.
It is another object of the present invention to provide a metal-bonded grinding tool and a manufacturing method therefor which can prevent the separation of the abrasive grains from the metal bond matrix and can prevent variations.in the grinding performance during a long period of time.
In accordance with an aspect of the present invention, there is provided a metal-bonded grinding tool comprising a base; and abrasive grains bonded to the base by a bond matrix containing Cu alloy as a main component; the bond matrix further containing a material selected from the group consisting of Ti, Al, and a mixture thereof; an average grain protrusion being set to 30% or more of an average grain diameter, wherein the distance from the surface of a deepest portion of the bond matrix between any adjacent ones of the abrasive grains to the peak of any one of the abrasive grains is defined as a grain protrusion; an average grain spacing being set to 200% or more of the average grain diameter.
Preferably, the Cu alloy is selected from the group consisting of bronze containing 10 to 33 wt % of Sn, brass containing 5 to 20 wt % of Zn, and aluminum bronze containing 5 to 20 wt % of Al. More preferably, the Cu alloy is composed of a plurality of different Cu alloys having the same main ingredient. The abrasive grains are selected from the group consisting of diamond, CBN (cubic boron nitride), SiC (silicon carbide), and cemented carbides powder.
According to the metal-bonded grinding tool of the present invention, the amount of projection of the abrasive grains from the metal bond matrix can be set very large. Accordingly, the removability of the chips of a workpiece from the tool can be improved, and the grinding resistance can be reduced because of no contact between the metal bond matrix and the workpiece. As a result, high grindability can be exhibited and good dissipation of grinding heat can also be ensured.
In accordance with another aspect of the present invention, there is provided a manufacturing method for a metal-bonded grinding tool, comprising the steps of kneading a Cu alloy powder selected from the group consisting of bronze containing 10 to 33 wt % of Sn, brass containing 5 to 20 wt % of Zn, and aluminum bronze containing 5 to 20 wt % of Al, a powder selected from the group consisting of Ti, Ti compound, Al, Al compound, and a mixture thereof, and an organic viscous material to obtain a paste mixture; applying the paste mixture to a base; depositing a given amount of abrasive grains to the paste mixture; heating the paste mixture to a given temperature in a high vacuum of 20 Pa or less to melt at least a part of the paste mixture; and cooling the paste mixture to solidify the at least a part melted, thereby bonding the abrasive grains to the base.
Preferably, the organic viscous material is selected from the group consisting of stearic acid, paraffin, and polyethylene glycol.
According to the manufacturing method of the present invention, chemical bonds are formed between the metal bond matrix and the abrasive grains, because Ti, Ti compound, Al, or Al compound has a reducing power to wet the abrasive grains. Accordingly, the abrasive grains can be strongly bonded to the metal bond matrix, thereby preventing the separation of the abrasive grains from the metal bond matrix.
Further, according to the manufacturing method of the present invention, the abrasive grains are scattered to be deposited on the paste mixture, so that the spacing between the abrasive grains can be freely adjusted. Accordingly, the present invention can be applied to a wide variety of work ranging from a hard material such as stone to a soft material that is prone to cause loading or clogging, such as wood cement board or FRP containing iron.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and with reference to the attached drawings should some preferred embodiments of the invention.